MONOGEAPIT OF THE GENUS 



DENTALIUM. 



Char. Gen. Molluseum corpore oblongo, testa elongate, tubu- 

 los&j conica, arcuata, ad apicem perforata; apertura circular!, 

 simplici ; operculo nullo. 



Tlie shells of this genus are regularly cmiicul curved tubes, open 

 at the apex, circular at the basal aperture. The worm-cases which 

 have the generic name Dilrupa, and which, of course, are not in- 

 cluded in this monograph, are distinguished from Denialium by 

 being swelled and contracted near the aperture, instead of being 

 gradually conical. 



Many species of Bentallum have a fissure at the dorsal edge 

 of the apical perforation. This being a somewhat irregular cha- 

 racter, even in individuals of the same species, and the fissure not 

 being formed in the growth of the shells, as in Emarglnula, but 

 merely by subsequent absorption or wearing, I cannot see in it a 

 sufficient indication of organic dilfcrence to justify the proposed 

 separation of the fissured species under the generic name " An- 

 talis." 



1. D. entale, Lhiu., f. 50, 51. 52. — Testa Isevi, solida, alba, 

 versus apicem rapide crescenti et arcuata, deinde rectiuscula et 

 magis cylindrica ; fissura parva. — White, smooth, solid, at first 

 acuminated and curved ; afterwards cylindrical and nearly straight. 

 Fissure only seen in young specimens. 



2. D. pretiosum, Nultall, f. 57. — Testa B. entail simillima, 

 sed angustiore, versus apicem haud tantum arcuata. — Less curved 

 and tapering near the apex than D. entale, and altogether more 

 cylindrical. The distinctness of the species is doubtful. 



3. D. lubiucatum, Soicb. TL, f. 56. — Testa polita, elongata, 

 alba, subpellucida, leviter arcuata, vix fissurata, gradatim creseente. 

 — Certainly a narrower shell, less solid,andof more gradual increase 

 than either of the preceding. 



VOL. III. I. 



